Nakanishi U.S. Pat. No. 3,603,088 teaches an ion thruster cathode in the form of a tube mounted in an encapsulated heater. Mirtich, Jr. et al U.S. Pat. No. 4,218,633 describes a hydrogen hollow cathode ion source which includes a cathode tube and a porous tungsten tube disposed coaxially therein. The space between these tubes is filled with an electrically conductive refractory material, and a heater is disposed around the outside of the cathode.
Seliger et al U.S. Pat. No. 4,301,391 is concerned with a dual discharge cathode that is directly heated. The cathode is made of barium impregnated in a porous tungsten.
Challoner et al U.S. Pat. No. 4,825,646 and Beattie U.S. Pat. No. 4,838,02 disclose an ion propulsion engine for use on a spinning spacecraft. The ion thruster is an electrostatic ion accelerator with an electron bombardment source. The ion thruster includes a cathode which is surrounded by a cathode heater.
Schumacher et al U.S. Pat. No. 5,075,594 discloses a plasma switch with a hollow thermionic cathode. The cathode is capable of self-heating by back ion bombardment. A Japanese Publication No. 1-244174 by Kawachi teaches a hollow cathode for electron impact type ion thrusters. A temperature controlling heater is provided in the circumferential part of a hollow cathode to secure an optimum working temperature.